using geometric morphometrics to test for fishing …mcnair.tamucc.edu/m.-bachner.pdf · 2021. 1....
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USING GEOMETRIC MORPHOMETRICS TO TEST
FOR FISHING-INDUCED SELECTION IN PHILIPPINE
RABBIT FISHDepartment of Life Sciences, Texas A&M University – Corpus Christi
Micah Bachner, Abner Bucol, Jason Selwyn, Christopher E. Bird
IntroductionPopulations experience a variable landscape of
selective pressures which act on phenotypic variation,
resulting in geographic variation in phenotypes.
Selective pressures applied by fishing activities
accelerate the pace of evolution and can affect
geographic variation in morphology. In the Philippines,
91% of locally-caught fishes are consumed locally, and
an estimated 56% of protein consumption comes from
fishes. In this region, Siganus fuscescens is a staple
food item that is eaten fresh, dried, or in the case of
juveniles, turned into a delicacy fish paste and whose
fishery is showing signs of collapse. To better
understand the effects of overfishing on the evolution
S. fuscenscens, here we test for differences in body
shape among four locations in Negros Oriental,
Philippines, each experiencing different fishing
regimes.
Results• Shape differed significantly among locations
-PC2 separates sites by size of operculum,
position of anal fin (DU-AY vs BA-AM)
-PC1 separates BA-AM by body depth
• 73% of variation in fishing pressure indices
explained by PC1
• Shape related to PC1 of fishing pressure indices
-Most fishermen in BA: deeper body, smaller
operculum
-Most people in DU: shallower, elongate body
Source df SS MS Rsq F Z P
Location 3 0.015 5.1E-3 0.14 9.0 9.1 1.0E-04
Resids 165 0.094 5.7E-4 0.86
Total 168 0.11
Table 1. Values from MANOVA test for differences in shape among locations.
Figure 2. Example photograph of S. fuscescens used for geometric morphometric analysis with landmarks (red points).
AcknowledgementsMarhuma Zaman, John Whalen, Dr. Rene
Abesames, Dr. Alcala, Dr. Kent Carpenter,
SUAKREM
Discussion• Significant differences in fish shape strongly
indicate spatial variation selective pressures.
• Population size and fisherman inversely related
perhaps due to more people = more subsistence;
fewer people = more commercial
• Phenotypes in area of highest commercial fishing
pressure may reduce chances of capture via net
-deeper body, smaller operculum
Figure 1. Map of sampling sites with accentuated municipality boundaries.
Inset table contains data on the number of people and fishers per hectare of
habitat.
Mean fish shape
Fish shape for max PC1
AMAYBADU
Methodsi. Specimens collected (n=166) from 4 fish markets
along the eastern coast of Negros Oriental (Fig. 1)
ii. All individuals photographed on left side
iii. 24 landmarks identified for each fish and stored in
TPS format
iv. A PCA of several indices of fishing pressure (pop
size, # fishers, available habitat, and distance from
pop center was used to isolate PC1 for comparison
with shape data
v. Geometric morphometrics using geomorph (Adams
and Otárola-Castillo 2013) R package: a) Procrustes
superimposition, b) MANOVA correction for allometry
and sex, c) MANOVA test for effect of location and
PCA to visualize, d) multivariate regression test for
effect of fishing pressure
Figure 4. A 1-D representation of fish shape regressed against fishing
pressure index. Regression scores were calculated from the multivariate
regression of landmarks against fishing pressure (Table 2, below). Bars
represent std. error and the shaded region is the 95% CI of the model.
Wireframes show the predicted shapes at the observed extremes of fishing
pressure. Here, sites are treated as independent observations, but fish are not.
Consequently, this test is conservative relative to that reported in Table 2.
Negros Island
Ayungon (AY); n=24
Bais (BA); n=87
Amlan (AM); n=31
Dumaguete (DU); n=24 30 km
12
3°E
Source df SS MS F P
Fishing
Pressure1 0.011 0.011 18.1